如何从HttpRequestException获取JSON错误消息

本文关键字：JSON 错误 消息 获取 HttpRequestException | 更新日期: 2023-09-27 17:51:01

我有一种情况，我必须在catch语句中提取响应(HttpResponseMessage)，但我认为不能这样做(在catch中使用await)。此外，如果我在捕获后这样做，HttpResponseMessage消息得到"处置"。代码:

 private async void MakeHttpClientPostRequest()
 {
     HttpResponseMessage response = null;
     try
     {
         HttpClient httpClient = new HttpClient();
         httpClient.Timeout = TimeSpan.FromSeconds(15);
         HttpContent httpContent = null;
         if (postJSON != null)
         {
             httpContent = new StringContent(postJSON);
             httpContent.Headers.ContentType = new MediaTypeHeaderValue("application/json");
         }
         response = await httpClient.PostAsync(url, httpContent);
         if (response != null)
         {
             response.EnsureSuccessStatusCode();
             netResults = await response.Content.ReadAsStringAsync();
         }
         if (this.convertedType != null)
         {
             MemoryStream assetReader = GetMemoryStreamFromString(netResults);
             assetReader.Position = 0;
             object value = fromJSON(assetReader, this.convertedType);
             networkReqSuccessWithObjectCallback(this, value);
         }
         else
         {
             //Return netResult as string.
             networkReqSuccessWithStringCallback(this, netResults);
         }
     }
     catch (TaskCanceledException)
     {
         ErrorException ee = null;
         ee = new ErrorException("RequestTimeOut");
         NotifyNetworkDelegates(ee);
     }
     catch (HttpRequestException ex)
     {
         //HERE I have to extract the JSON string send by the server
     }
     catch (Exception)
     {
     }
}

这里可以做什么?

以前使用HttpWebRequest:

的方法
public void MakePostWebRequest()
{
    //WebCalls using HttpWebrequest.
    HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(url);
    request.CookieContainer = new CookieContainer();
    request.ContentType = "application/json";
    request.Method = "POST";
    requestState = RequestState.ERequestStarted;
    asyncResult = request.BeginGetRequestStream(new AsyncCallback(GetRequestStream), request);
}

private void GetRequestStream(IAsyncResult asyncResult)
{
    HttpWebRequest request = (HttpWebRequest)asyncResult.AsyncState;
    {
        try
        {
            Stream requestStream = request.EndGetRequestStream(asyncResult);
            if (request != null)
            {
                using (requestStream)
                {
                    StreamWriter writer = new StreamWriter(requestStream);
                    writer.Write(postJSON);
                    writer.Flush();
                }
            }
        }
        catch (WebException we)
        {
        }
    }
}
private void GetResponseStream(IAsyncResult asyncResult)
{
    requestState = RequestState.EResponseStream;
    HttpWebRequest request = asyncResult.AsyncState as HttpWebRequest;
    HttpWebResponse response;
    try
    {
        response = (HttpWebResponse)request.EndGetResponse(asyncResult);
        using (StreamReader reader = new StreamReader(response.GetResponseStream()))
        {
            netResults = reader.ReadToEnd();
        }
        requestState = RequestState.ERequestCompleted;
    }
    catch (WebException we)
    {
        // failure
        ErrorException ee = null;
        response = we.Response as HttpWebResponse;
        if (response != null)
        {
            using (StreamReader reader = new StreamReader(response.GetResponseStream()))
            {
                //HERE I'm getting the json error message
                netResults = reader.ReadToEnd();
            }
        }
    }
    catch (Exception e)
    {
        networkReqFailedCallback(this, e);
    }
}

如何从HttpRequestException获取JSON错误消息

我强烈怀疑问题是异常是实际上是抛出的调用EnsureSuccessStatusCode，其文档包含:

如果Content不为空，此方法还将调用Dispose来释放托管和非托管资源。

基本上听起来，如果你需要失败时的内容，就不应该使用这个方法来确定成功或失败。

只需自己检查状态代码，并根据该代码适当地使用内容。注意，在catch块中，如果请求完全失败，response很容易为null。

正确的方法是在try块本身

try
{
    response = await httpClient.PostAsync(url, httpContent);
    netResults = await response.Content.ReadAsStringAsync();
     //do something with the result
}
catch(HttpRequestException ex)
{
     // catch any exception here
}

Catch块用于处理异常条件。如果需要重新抛出，但应该避免。

Response应该只在远程服务器实际响应的情况下可用。如果响应是null(我理解这是你的情况)，这意味着由于某些原因，请求没有交付或响应没有收到(不衡量哪个响应-代码200 (OK)或任何其他代码(错误))。请检查错误代码(we.Status)。确保它等于WebExceptionStatus.ProtocolError(即，服务器响应错误);

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